Generally, compression coding means a series of signal processing for transmitting digitalized information via a communication circuit or storing the digitalized information in a format suitable for a storage medium. There exist audio, video, characters and the like as targets for compression coding. Particularly, a scheme for performing compression coding on video is called video sequence compression. And, a video sequence is generally characterized in having spatial redundancy and temporal redundancy.
Specifically, a scalable-video-coded bit stream can be decoded partially and selectively. For instance, a decoder having low complexity is capable of decoding a base layer and a bit stream of a low data rate is extractable for transport via network having a limited capacity. In order to generate an image of high resolution more gradually, it is necessary to enhance a quality of image step by step.